Limonene

Limonene, a colourless liquid abundant in the essential oils of pine and citrus trees and used as a lemonlike odorant in industrial and household products and as a chemical intermediate.

Limonene exists in two isomeric forms (compounds with the same molecular formula—in this case, C10H16—but with different structures), namely l-limonene, the isomer that rotates the plane of polarized light counterclockwise, and d-limonene, the isomer that causes rotation in the opposite direction. In the extraction of citrus juices d-limonene is obtained as a by-product, and it also occurs in caraway oil; l-limonene is present in pine needles and cones; dl-limonene, or dipentene, the mixture of equal amounts of the l- and d-isomers, is a component of turpentine.

Dipentene may be sulfurized to produce additives that improve the performance of lubricating oils under heavy loads; d-limonene is commercially converted to l-carvone, which has a caraway-seed flavour.

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...in the essential oils of trees and other plants. (Essential oils are responsible for the characteristic odour, or “essence,” of the plant from which they are obtained.) Myrcene and limonene, for example, are alkenes found in bayberry and lime oil, respectively. Oil of turpentine, obtained by distilling the exudate from pine trees, is a mixture of hydrocarbons rich in...

...leads to monocyclic, bicyclic, and further subclasses in which one, two, or larger numbers of rings are present. This further classification is exemplified by β-myrcene, an acyclic monoterpene; limonene, a monocyclic monoterpene; α-pinene, a bicyclic monoterpene; and vitamin A, an oxygenated monocyclic diterpene. The dotted lines in the structural formulas indicate the division of the...

...of plants contain the polyterpene hydrocarbons rubber or gutta-percha. Certain other species, including related species, of plants may be characterized by the presence of menthol, citral, camphor, limonene, or α-pinene.